This invention is generally directed to a method and apparatus for dispersal of aggregates of red and white blood cells and platelets. The present invention employs a sonic or ultrasonic device to efficiently breakup aggregates of red and white blood cells and platelets by driving the ultrasonic signal over a small range of frequencies around the acoustic slow wave frequency of the agglomerate. At this frequency, the fluid vibrates out of phase with the solid and is forced out through the pore structure in the agglomerate.
Compressional ultrasonic waves Interact with particle aggregates, whether they are aggregates of blood cells or aggregates of pigment particles, in a limited number of ways. Each way can have its own set of technological advantages and disadvantages that make it suitable for some applications, and unsuitable for others. For example, the pressure within an ultrasonic wave is at a maximum at one location within the wave, called the peak, and at a minimum xc2xd wavelength away, at the valley. There is a stress exerted on a particle aggregate due to this difference in pressure. If that stress exceeds the yield stress of the aggregate, particle breakup occurs. However, for a compressional wave velocity of 1520 m/sec (velocity of sound in water) and a frequency of 10,000 Hz the wavelength is 15.2 cm. This approach is not appropriate for breaking up blood cell aggregates.
Another approach to breaking up particle aggregates is by inducing cavitation. If the amplitude of the pressure wave is sufficient, and the frequency is in the appropriate optimum range, dissolved gases can be pulled from solution to form microscopic bubbles, which grow and then collapse under the influence of the pressure wave. The dynamics of this process is governed by the Kirkwood-Bethe equation. For fluids such as water and blood serum, the maximum for cavitation generation frequency occurs around 20 kHz, with an overtone at around 40 kHz. Required pressure amplitudes are on the order of a few tenths of an atmosphere. However, when cavitation bubbles collapse pressures on the order of 104 atmospheres can be generated. These stresses do very well in breaking up particle aggregates. However, these pressures far exceed the yield stresses of cell membranes, and so cavitation can do considerable damage to biological specimens, including blood.
Therefore there is a need for a method and apparatus for dispersal of aggregates of red and white blood cells which overcomes the beforementioned problems
There is provided a method for dispersing aggregates in a liquid medium including blood the method comprising: holding aggregates in said liquid medium in a vessel; applying a predefined acoustic slow wave frequency near said vessel for separating the aggregates in said liquid medium, said applying includes selecting a type aggregates to be dispersed in said liquid medium, determining said predefined acoustic slow wave frequency of said selected aggregates. Wherein determining said predefined said acoustic slow wave frequency includes calculating said predefined said acoustic slow wave frequency by the following equation:
xe2x80x83fc=xcex7{Sv2(1xe2x88x92xcfx86)2}/(2xcfx80B xcfx862 xcfx81f)
Where fc is the acoustic slow wave frequency, xcex7 is the fluid viscosity, Sv is the primary particle surface area per unit volume of the aggregate, xcfx86 is the aggregate porosity, xcfx81f is the fluid viscosity, and B is a phenomenological constant.
The aggregates include red blood cells, white blood cells or platelets.